1. Field of the Invention
This invention relates to an apparatus for positioning a transducer, such as a magnetic head, for recording, reproducing or erasing information on a medium, and more particularly to an apparatus for both enough fine positioning and high-speed shifting of the transducer.
2. Description of the Prior Art
In recent years, systems such as an electronic still camera or a still video floppy disc player have been developed for recording still video signals on a floppy disc, a so-called disc pack, and reproducing the recorded images on a television tube. In order to record video information on a floppy disc, there are two types of recording techniques: field recording and frame recording. In field recording, the information for one field is recorded on one track to form a field picture. In frame recording, the information for a first field is recorded on one of two adjacent tracks (for example, the outer track) and the information for a second field is recorded on the other track (for example, the inner track), thus one frame of picture is obtained from the information for the first and second fields recorded on a pair of tracks.
For the electronic still cameras, uniform standards have been already established by THE ELECTRONIC STILL CAMERA CONFERENCE with respect to various items such as video recording format, etc. According to the standards, both field recording and frame recording are allowed for recording video signals on a magnetic recording medium (floppy disc). Therefore, it is provided that the data for discriminating between field recording and frame recording should be prerecorded so that the type of recording can be identified at the time of reproducing the image. The signal recorded for enabling the identification is called an identification (ID) code and is multiplexed with the video signal on the recording medium. That is, it is provided that a frame type recorder should make the frequency multiplexing of the ID codes of the field/frame recording on the video track. According to the standards, the frequency of the carrier for the recording of the identification data is 13 times the horizontal sync frequency f.sub.H (i.e., 204.54 KHz in the NTSC system), the modulation system is DPSK (Differential Phase Shift Keying), and the bit rate is such that one bit corresponds to the interval of 4H (H represents one horizontal scanning line period). (See NIKKEI ELECTRONICS, Jul. 2, 1984, etc.)
Further, bit allocation of ID codes is made as shown in FIG. 1. An interval of 4H (i.e., the interval of one bit) after the start point (front edge) of vertical synchronizing signal (V. SYNC) is an initial bit and the interval of 8H (i.e., the interval of two bits) following the initial bit is assigned for the ID codes of the field/frame recording. The data "00" in the two bit interval correspond to field recording and the data "01" or "10" correspond to frame recording. In the latter case, the data "01" and "10" represent the outer and inner tracks of a pair of frame-recorded tracks, respectively.
As explained above, the recording of a video signal on a floppy disc in an electronic still camera is made together with the ID code signal for each recording track and field and frame recordings may often coexist on the same floppy disc. As is well known, it is possible to rewrite or erase recorded information on a desired track of a floppy disc. However, in a floppy disc where field and frame recordings coexist, a problem arises when the information recorded on an arbitrary track is erased. If the erased track is a field-recorded track, video information for one frame of picture is erased, which causes no concern. However, if the erased track is one of a pair of frame-recorded tracks, the other track remains unerased. The unerased track continues to have the ID code signal representing that it is one of a pair of frame-recorded tracks (for example, the outer track). When the unerased track is reproduced, it is identified as a frame-recorded track and either two different images or one field image and an unrecorded portion will be reproduced as one frame of picture, which causes inconvenience.
It is desirable that a system for erasing information recorded on a track should be capable of providing a control for the head positioning and exciting based on the ID codes previously detected from record tracks intended to be erased, so as to automatically erase a group of tracks on which respective parts of a unitary amount of information are recorded. A specific example of such a system will be suitably applicable to erase a pair of frame recorded tracks on a video floppy disc based on the ID codes recorded with the video signal using the frequency division multiplexing method. As explained above, in conformity with the standard specifications for a recording system on a magnetic disc, the Still Video Floppy System provided by THE ELECTRONIC STILL CAMERA CONFERENCE, the ID code indicates whether a track played back consists of a field picture or a frame picture, and this code shall be recorded whenever a frame picture is recorded. An example of such a system should comprise means for detecting ID code so as to determine whether a track to be erased is a field recorded track or a frame recorded one and further determine whether a frame recorded track is an outer side track or an inner side track. Then, the system takes appropriate action to erase a pair of frame picture tracks entirely including one previously intended to be erased based on the above-mentioned determination.
On the other hand, in case recorded information on a track is erased by utilizing a head having a head gap with its width substantially equal to the width of the track, several parts of the recorded information or signals still remain edgewise in the track due to eccentricity for setting of the floppy disc, expansion and contraction or warp of the floppy disc, or a probable error for head positioning which occurs in the other corresponding apparatus employed to erase the information on that track.
It has been proposed for such a system to entirely erase recorded information on a track by shifting the erase head in a direction traversing the track while rotating a recording medium (that is, floppy disc) in a plurality of turns (see Published Japanese Utility Model Application, Publication No. 57-21133). A fine pitch shifting operation is desired to accomplish such a purpose as mentioned above. A fine pitch shifting operation is also desired to control head position so as to regularly trace a track formed on the recording medium.
However, in a conventional system, when a motion converting device having such characteristics that a large amount of primary (input) motion causes a small amount of secondary (output) motion is employed for a fine pitch shifting operation of the head, a high-speed head access (that is, head shifting from one track to the next) is inevitably sacrificed.